1. Field of the Invention
The invention relates to the mixing of materials and particularly foods which are shear sensitive, thereby to prevent damage to the foods and to maintain the organoleptic and visual qualities of the food.
2. Description of the Prior Art
Large scale cooking of food such as is necessary in institutional situations and the like has long been accomplished in large cooking kettles, cooking or heating of foodstuffs in such kettles often requiring stirring or mixing operations which occur while the foodstuffs are being heated or cooked. Since mixing or stirring by hand is unreasonably laborious even in the smaller kettles used in hotels, restaurants, health and care facilities and the like, the use of power driven mixers has long been known. Such mixers often take the form of structural elements which merely stir a food or other material which is to be mixed either with or without cooking or heating. Conventional mixing agitators also exist which not only mix food materials being cooked or heated in a kettle, but also scrape the surfaces of the kettle which contact the food materials to prevent the sticking of overheated food materials to surfaces of the kettle which can occur due to localized overheating of the food materials which simple stirring often cannot prevent. Accordingly, mixing agitators having scraper elements which contact food-contacting surfaces of cooking kettles have previously been provided in the art, such mixers acting not only to scrape the walls of the kettle to displace food materials positioned adjacent the walls but which also act to mix and blend the remaining portions of the body of the food materials.
Mixing agitators having scraping capability are disclosed by Groen, Jr. in U.S. Pat. No. 3,752,057, this patent describing a mixer having a shaft which extends into a kettle at an angle of at least 20.degree. with respect to the vertical axis of the kettle. The shaft of Groen, Jr. is provided with a hoop-like structure at the distal end of the shaft, the hoop-like structure having a plurality of scrapers pivotally mounted to said structure at differing inclinations to the axis of the shaft, the scrapers acting to contact surface portions of the kettle in order to prevent food "burn-on" when a food material is being heated within a cooking kettle.
Giusti, in U.S. Pat. No. 4,199,266, describes a mixing agitator having scraping capability wherein a rotary shaft is disposed horizontally within a cooking kettle, the shaft having a substantially circular agitator mounted thereon and wherein the agitator is formed of a pair of substantially annular semicircular blades each having an internal segment-shaped web. The annular blades each carry a plurality of scrapers at their respective peripheries for scraping of internal surfaces of a kettle.
Both the Groen, Jr. and Giusti patents act to move cooking foods from the bottom of a kettle at which location the greatest amount of heat is being directed into the cooking material and lifts the food material to the vicinity of the uppermost portion of the body of the food material, thereby giving that food material near the top of the kettle a chance to flow downwardly and into contact with the heated surfaces of the kettle at the bottom of the kettle. A mixing and blending of the material thus occurs with the scraping of the walls of the kettle being intended to assure that no portion of the food material remains near the cooking surfaces for a time sufficient to cause overheating of portions of the food material.
Examples of other mixing agitators, some of which include scraping elements, are disclosed by Rebechini in U.S. Pat. No. 2,753,158; Hirshon in U.S. Pat. No. 2,580,780; Costa et al in U.S. Pat. No. 3,739,710; and Addison in U.S. Pat. No. 3,731,339. With the exception of the Costa et al patent, the mixers described above do not employ agitators having a vertical axis since such vertical axis agitators must function at high speed to effectively mix certain foods which consist of solid pieces in a liquid base. Operation of such mixers at high speed exerts a substantial shearing affect on the solid materials in such a mixture, thereby resulting in fragmentation and damage to such solid pieces when the solid pieces are of a sensitive nature. Accordingly, in many food mixing situations, mixing at a low speed is necessary in order to prevent physical degradation of the food. Accordingly, a general lifting of food materials near the bottom of a cooking kettle is required in order to prevent damage to shear-sensitive food materials in a mixture which is either being simply mixed or mixed during a cooking or heating process. While agitators including agitators having a scraping capability have been previously utilized in the art as indicated above, such mixing agitators have been intended to be "universal" in operation, that is, such agitators have attempted to be applied to differing applications as diverse as particular mixing needs in food processing, chemical processing, cosmetics mixing, pharmaceutical processing and the like. Agitator structures designed to function in these various applications typically are not well adapted for optimum usage in any of said applications but are typically only barely adequate. The present mixing agitator is particularly designed for use in food processing and is particularly intended for use in the mixing of foods which are being cooked in a kettle such as a steam-jacketed kettle with the foods either having a water base or roux base with thickeners. The scraping capability of the present mixing agitator is particularly necessary for the roux-base materials to prevent "burn-on" during cooking. For those food materials not particularly subject to the burn-on problem or for food materials which need merely to be mixed, the present mixing agitator can be used with or without scraping elements to gently and thoroughly mix such food materials. While the present mixing agitator can be employed in fields other than food processing with performance at least equal to commercially available agitators such as are exemplified by the structures described in the above-noted patents, the present mixing agitator is particularly useful in the food processing field and allows extremely thorough and gentle mixing of food materials including scraping thereof with a relatively simple and inexpensive structure capable of rotating in both clockwise and counter clockwise direction. Further, the present mixing agitator can be rapidly assembled and disassembled in a cooking kettle without the use of tools, thus facilitating cleaning of the agitator and kettle and reducing the time required between cooking of different materials within the same kettle. Accordingly, the present invention provides a mixing agitator which includes a scraping capability and which provides performance, operational and cost advantages over agitators of the prior art.